A TFT-LCD (Thin Film Transistor Liquid Crystal Display) or an OLED (Organic Light Emitting Diode) display is provided with an array substrate, wherein the array substrate can be divided into a display region and a wiring region located at the periphery of the display region. The peripheral region is provided with a gate driver configured for progressively scanning gate lines. The existing gate drivers usually adopt a GOA (Gate Driver on Array) design in which a TFT (Thin Film Transistor) gate switching circuit is integrated in the peripheral region to constitute a GOA circuit, thereby achieving a narrow frame design.
The GOA circuit includes a plurality of cascade shift register units, and an output terminal of each of the cascade shift register units is connected to a row of gate lines. During progressive scanning of the gate lines by the GOA circuit, a signal output terminal OUTPUT(n) of a certain level shift register unit RSn outputs a gate scanning signal to a gate line Gn so as to complete the scanning of the gate line Gn. When a signal output terminal OUTPUT (n+1) of a next level shift register unit RS(n+1) outputs a gate scanning signal, a potential of the signal output terminal OUTPUT (n) of the previous level shift register unit RSn needs to be pulled down to a low level, thereby ensuring that no scanning signal is outputted from the signal output terminal OUTPUT (n).
When only one pull-down circuit is provided in the shift register unit, the pull-down circuit is required to be in a working state during the non-output phase of the shift register unit, thereby causing the TFT in the pull-down circuit to be in an ON state for a long period of time. As a result, the characteristics of the TFT are attenuated and the lifetime of the GOA circuit is reduced. In order to solve this problem, a plurality of alternately operated pull-down circuits is usually provided in one shift register unit in the related art. However, if one of the plurality of the alternately operated pull-down circuits is damaged, the GOA circuit will not be able to work properly.